Studies dealing with the mechanism of action of compounds of interest as anti-cancer agents, and the basis of resistance to these agents, will be continued using mammalian cells growing in vitro. Previous studies have established that rapidly growing mouse fibroblasts and mouse lymphoma cells are inhibited by glucocorticoids in vitro, and the earliest biochemical alterations that have been detected so far have to do with the rates of glucose uptake and metabolism in these cells. We have developed extensive investigations into the nature of the steroid hormone receptor macromolecule found in these cells. The methods employed use high specific activity triamcinolone acetonide, a potent synthetic glucocorticoid, as a radioactive marker which binds to receptor material, and separating free from bound steroid on small Sephadex G-25 columns. We propose to extend our investigations of this receptor macromolecule, developing information in three specific areas: (1) purification of receptor material and physicochemical characterization of the macromolecule; (2) studies on nuclear- cytoplasmic translocations of the receptor macromolecule, and the energy and temperature dependence of such translocations; and (3) exploration of biochemical mechanisms by which the steroid-receptor complex initiates the biological effect, inhibition of growth rate. In all of these studies, the availability of a steroid-resistant subline of these cells will allow useful comparative studies to be made. It is already known that the steroid-resistant cells have much reduced amounts of receptor in the cytosol cellular fraction. It will be of interest to determine if this is due to a decreased rate of synthesis of this material, enhanced degradation, or alterations in the complex translocations of this receptor within the cell.